This invention relates to improved flexible self-heating packages that can be used to heat or warm liquid, semi-liquid, or solid products, or to maintain the temperature of products sold hot, to make them more suitable for their intended use. The self-heating device is one in which a solid or semi-solid heat-producing composition is reacted with an activating liquid, typically water or an aqueous solution, to generate heat. A number of self-heating containers have been reported, but all suffer from disadvantages that decrease their convenience of use or increase the expense for their manufacture.
U.S. Pat. No. 5,628,304 Freiman et al (1997) reports a recyclable self-heating container having two compartments which contain anhydrous calcium chloride and water, respectively. The container is provided with a cutting device that is used to open the water compartment and allow water to contact the anhydrous calcium chloride and release heat.
U.S. Pat. No. 4,773,389 Hamasaki et al. (1988) reports a self-heating foodstuff container having a body with two chambers, a liquid container and a support member. One of the chambers of the body is provided to receive a foodstuff and the second is provided to receive an exothermic reaction agent. The heater is activated by sliding a support member in contact with the body to cause the liquid to be discharged into the second chamber to initiate exothermic reaction.
U.S. Pat. No. 4,793,323 Guida et al. (1988) reports a single-use self-heating container ith a plastic vessel within and attached to an external insulated envelope. Two compartments, an upper and a lower compartment, are provided in the vessel separated by a membrane. The upper compartment contains a solid reactant and the lower contains an activating liquid. The exothermic reaction is initiated by actuating a membrane-breaking member in the liquid compartment. The upper compartment of the vessel optionally contains a temperature control substance which undergoes a phase change between 90.degree. C. and 100.degree. C.
U.S. Pat. No. 4,809,673 Charvin (1989) reports a device for heating food having an upper compartment for receiving food and a lower compartment in which two reagents are separated from each other by one or more watertight partitions. The device is provided with internal radial blades operated from outside of the container by an external control knob to tear the watertight partitions and initiate the exothermic reaction.
U.S. Pat. No. 5,220,909 Pickard et al. (1993) reports a self heating individual meal module includes a tub for holding food to be heated. The tub is welded to a tray and in contact with a pad of an electrolytic-solution-activated exothermic-chemical. The heater also has a pouch containing an electrolytic solution. A pull-tab is provided on the pouch to release the electrolytic solution to activate the chemical pad to generate heat.
U.S. Pat. No. 5,255,812 Hsu (1993) reports a self-heating tin container having a chemical compound for releasing heat upon mixing with a liquid catalyzer. The tin has a cap having an internal compartment containing liquid catalyzer and a pin on its inside surface which is used to pierce the internal compartment and allow liquid catalyzer to contact the chemical compound in the tin. Pressing an elastic top edge of the cap when in place on the tin, causes the pin to pierce the compartment permitting the liquid catalyst to flow into the tin.
U.S. Pat. No. 4,057,047 of Gossett (1977) reports a thermal pack in which heat or cold is generated by contacting water with selected chemicals to generate an exothermic or an endothermic reaction. The thermal pack has three bags, two of which form the outer surface and inner surface of the pack, respectively. The inner of these bags holds the chemicals that will react with water. A third smaller bag containing water is inserted into the inner bag which contains the chemicals. The inner bag is ruptures by hand pressure to release water and activate the chemicals. The smaller inner bag is provided with a marginal seal that facilitates rupture on application of hand pressure.
While a number of self-heating devices have been described, there is a continuing need in the art for devices that are more convenient to use and less expensive to manufacture. Many prior art devices require an additional device element, such as a pin or serrated edge, to bring the heater components into contact to generate heat. This requirement adds to the inconvenience and expense of the device. Other prior art self-heating devices are constructed with one or more rigid pieces that again generally increase cost and add to the bulk of the device.